Core drill

ABSTRACT

A plurality of chip evacuating grooves ( 16, 26, 36, 46   a,    46   b ) in a vertical direction in parallel with a rotational axis of a core main body ( 14 ) are formed at an outer peripheral face of the core main body ( 14 ) in a circumferential direction from a lower end portion to an upper end portion of the core main body ( 14 ) in a cylindrical shape provided with a drilling blade ( 15 ) at a lower end edge thereof. Further, a sectional area of the chip evacuating groove ( 16 ) is formed to gradually increase from a lower end to an upper end of the core main body ( 14 ). Further, a number of projections ( 52, 62, 70, 72 ) are formed at the outer peripheral face of the core main body ( 14 ) between the chip evacuating grooves.

TECHNICAL FIELD

The present invention relates to a core drill for concrete for boring acomparatively large through hole for piping to concrete, a stonematerial or the like constituting a wall or a foundation of a buildingor the like.

BACKGROUND ART

A core drill has conventionally been used for boring a comparativelylarge hole for passing a water pipe, a gas pipe or a pipe for an airconditioner to a wall, a floor, a foundation or the like constituted byconcrete, a stone material or the like in constructing or adding orreforming a building. A core drill is attached with drilling bladesformed by sintering diamond abrasive grains by a metal bond at a lowerend edge of a core main body formed in a cylindrical shapecircumferentially at intervals and by pressing the drilling blades to aconcrete face and rotating the core main body, a groove in a shape of acircular ring is cut to form at concrete or the like and by cutting thegroove gradually deeply, a hole penetrating concrete or the like isbored. The core drills are used in tools of a wet type cutting the holeby supplying a fluid for cooling to the drilling blades and a dry typewhich does not supply the cooling fluid.

In drilling operation by the core drill, when the drilling blades formedat a front end thereof cut concrete, a stone material or the like, alarge amount of chips of concrete or the like is produced. When thechips are clogged between the core main body and an inner wall face ofthe bored hole, a resistance against rotating the core drill isincreased to thereby reduce a drilling efficiency. Although when thecore drill is used in the wet-type tool, the chips are evacuatedcomparatively efficiently by operation of making the cooling fluid flow,in operation by the dry type tool, the chips may not be evacuatedsufficiently to thereby prolong an operational time period of boring.

Therefore, according to a core drill of a background art, an outerperipheral face of a core main body is formed with a chip evacuatinggroove in a spiral shape and chips produced by drilling blades at afront end thereof are evacuated to an upper side of the core main bodyvia the groove by rotating the core drill (refer to, for example,JP-B-06-092083). Further, there is known a core drill improvingevacuation of chips by forming an abrasive grain layer at a surface of aprojected streak portion formed at an outer peripheral face of a coremain body formed with a groove for evacuating chips and further finelygrinding chips produced at drilling blades at a front end thereof by theabrasive grain layer (refer to, for example, JP-A-2000-309013)

According to the core drill of the background art, the chip evacuatinggroove for evacuating chips is formed in the spiral shape at the outerperipheral face of the core main body and therefore, there poses aproblem that production cost is increased by requiring a number of stepsin working by, for example, a lathe in producing the core main body.Further, according to the core drill of the background art, the groovefor evacuating chips is formed by the same sectional area from a frontend side to an upper end of the core drill and therefore, there poses aproblem that operation of evacuating chips is not sufficiently carriedout, chips formed at the front end portion is compressed to clog atinside of the groove, and the chips are brought into close contact witha wall face of the cut hole of concrete to thereby hamper the drillingefficiency.

Further, according to a hand-held tool for carrying out drillingoperation by grabbing the tool by the hand, the outer peripheral face ofthe core main body is brought into contact with an inner wall face of aconcrete hole in a wide area by swinging an axis line of the core drilland therefore, there also poses a problem that a drilling function isreduced by reducing a rotational speed of the core drill by increasing afriction resistance. In order to rotate the core drill at high speedagainst the friction resistance, a large-sized tool having a largerdriving force needs to use.

DISCLOSURE OF THE INVENTION

It is a problem of the invention to resolve the above-described problemof the background arts and provide a core drill facilitating productionand capable of reducing cost. Further, other problem of the invention isto provide a core drill capable of evacuating chips produced by adrilling blade efficiently to an upper side even when a dry type tool ais used and capable of promoting a drilling function by reducing afriction resistance between the core drill and an inner peripheral faceof a concrete hole.

In order to resolve the former problem, the invention is characterizedin a core drill including a shank connected to a rotating tool at anupper end thereof and constituted by a core main body in a cylindricalshape provided with a drilling blade at a lower end edge thereof,wherein a plurality of streaks of chip evacuating grooves in parallelwith a rotational axis of a core main body are formed at an outerperipheral face of the core main body at intervals in a peripheraldirection from a lower end portion to an upper end portion of the coremain body in the cylindrical shape.

Further, the core drill according to the invention is characterized inthat the chip evacuating groove is formed such that a sectional areathereof is gradually increased from the lower end portion to the upperend portion.

Further, the core drill according to the invention is characterized inthat an opening for communicating inside and outside of the core mainbody is formed at a bottom of the chip evacuating groove.

Further, in order to achieve the latter problem, the invention ischaracterized in a core drill including a shank connected to a rotatingtool at an upper end thereof, constituted by a core main body in acylindrical shape provided with a drilling blade at a lower end edgethereof and formed with a chip evacuating groove at an outer peripheralface of the core main body from a lower end portion to an upper endportion of the core main body in the cylindrical shape, wherein asectional area of the chip evacuating groove is formed to graduallyincrease from a lower end to an upper end of the core main body.

Further, the core drill according to the invention is characterized inthat the chip evacuating groove is formed in a spiral shape at the outerperipheral face of the core main body.

Further, the core drill according to the invention is characterized inthat an opening for communicating inside and outside of the core mainbody is formed at a bottom of the chip evacuating groove.

Further, the core drill according to the invention is characterized inthat a slender groove is formed at the outer peripheral face of the coremain body between contiguous ones of the chip evacuating grooves andfrom the lower end portion to the upper end portion of the core mainbody.

Further, the core drill according to the invention is characterized inthat a lateral groove is formed at the outer peripheral face of the coremain body between contiguous ones of the chip evacuating grooves and ina circumferential direction of the core main body.

Further, a core drill according to the invention is characterized in acore drill including a shank connected to a rotating tool at an upperend thereof and constituted by a core main body in a cylindrical shapeprovided with a drilling blade at a lower end edge thereof, wherein aplurality of streaks of chip evacuating grooves extended from a lowerend portion to an upper end portion of the core main body in thecylindrical shape are formed at an outer peripheral face of the coremain body along a circumferential direction and a number of projectionsprojected from the outer peripheral face of the core main body in aradial direction are formed at the outer peripheral face of the core inthe cylindrical shape between contiguous ones of the chip evacuatinggrooves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a core drill according to an embodimentof the invention.

FIG. 2 is a vertical sectional view of a core drill the same as that inFIG. 1.

FIG. 3 is a sectional view showing a state of drilling concrete by thecore drill of the embodiment of FIG. 1.

FIG. 4 is a perspective view of a core drill according to otherembodiment of the invention.

FIG. 5 is a perspective view of a core drill according to otherembodiment of the invention.

FIG. 6 is a perspective view of a core drill according to still otherembodiment.

FIG. 7 is a perspective view of an example of forming a slender grooveat an outer peripheral face between chip evacuating grooves.

FIG. 8 is a perspective view of an example of forming a lateral grooveat an outer peripheral face between chip evacuating grooves.

FIG. 9 is a perspective view of a core drill according to otherembodiment of the invention.

FIGS. 10(a), 10(b) and 10(c) show details of a projection of the coredrill of FIG. 9, FIG. 10(a) is a perspective view, FIG. 10(b) is a frontview and FIG. 10(c) is a sectional view.

FIG. 11 is a perspective view of a core drill according to still otherembodiment of the invention.

FIGS. 12(a), 12(b) and 12(c) show details of a projection of the coredrill of FIG. (11), FIG. 12(a) is a perspective view, FIG. 12(b) is afront view and FIG. 12(c) is a sectional view.

FIGS. 13(a), 13(b) and 13(c) show other embodiment of a projection, FIG.13(a) is a perspective view, FIG. 13(b) is a front view and FIG. 13(c)is a sectional view.

FIGS. 14(a), 14(b) and 14(c) show still other embodiment of aprojection, FIG. 14(a) is a perspective view, FIG. 14(b) is a front viewand FIG. 14(c) is a sectional view.

Further, in notations in the drawings, numeral 10 designates a coredrill, numeral 11 designates a shank, numeral 12 designates a drill mainbody, numeral 13 designates an upper end portion, numeral 14 designatesa core main body, numeral 15 designates a drilling blade, numeral 16designates a chip evacuating groove, numeral 17 designates a groovebottom portion, numeral 18 designates an opening, numeral 20 designatesa core drill, numeral 26 designates a chip evacuating groove, numeral 30designates a core drill, numeral 36 designates a chip evacuating groove,numeral 40 designates a core drill, notation 46 a designates a chipevacuating groove, notation 46 b designates a chip evacuating groove,numerals 50, 60 designate core drills, numerals 51, 61 designate chipevacuating grooves, numerals 52, 62, 70, 72 designate projections, andnumeral 53, 63, 71,73 designate top portions.

Best Mode for Carrying Out the Invention

An explanation will be given of a mode for carrying out the inventionbased on embodiments shown in the drawings as follows. FIG. 1 shows thecore drill 10 according to a first embodiment of the invention which isconstituted by the shank 11 coupled to a rotating tool and transmittedwith a rotating force similar to the background art, and the drill mainbody 12 coupled to a lower end portion of the shank 11. The drill mainbody 12 is constituted by the core main body 14 in a cylindrical shapethe upper end portion 13 of which is closed, and a plurality of drillingblades 15 attached to a lower end edge of the core main body 14 atintervals in a circumferential direction. The drilling blade 15 ismolded in a tip-like shape by sintering a metal bond mixed with diamondabrasive grains and the drilling blades 15 are bonded to the lower endedge of the core main body 14 by welding at equal intervals in aperipheral direction.

A plurality of the chip evacuating grooves 16 extended in a verticaldirection in parallel with a rotational axis of the core drill areformed at an outer peripheral face of the core main body 14 atpredetermined intervals in the peripheral direction. By forming the chipevacuating groove 16 in parallel with the shaft of the core main body 14in this way, in comparison with the groove in the spiral shape of thebackground art, working by a lathe or the like is not needed,fabricating steps are simplified and fabrication cost or the like can bereduced.

Further, according to the embodiment, as shown by FIG. 2, the chipevacuating groove 16 is cut to gradually change a depth thereof suchthat a depth L2 of the chip evacuating groove at the upper end portion13 is larger than a depth L1 of the chip evacuating groove at the lowerend portion proximate to the drilling blades 15 to thereby form the chipevacuating groove 16 such that a sectional area thereof is increased toan upper side. Therefore, in pushing up chips at inside of the chipevacuating groove 16 to the upper side by chips produced by the drillingblades 15 at the lower end portion of the core main body 14, chips areprevented from being clogged at inside of the chip evacuating groove 16at the widened upper portion.

Further, the groove bottom portion 17 of the chip evacuating groove 16is formed with the opening 18 for communicating inside and outside ofthe cylinder of the core main body 14 and air compressed on an innerside of the core main body 14 by progressing drilling by the core drill10 is exhausted to an outer side of the core main body 14. At thisoccasion, compressed air to be exhausted is exhausted into the chipevacuating groove 16 and therefore, compressed air is not hampered frombeing exhausted and operation of evacuating chips at inside of the chipevacuating groove 16 to the upper side is promoted by a flow ofcompressed air to be exhausted.

FIG. 3 shows a state in the midst of drilling operation by the coredrill 10 in the above-described embodiment. By rotating the core drill10, a surface of concrete C is cut by the drilling blades 15 to therebyform a groove in a ring-like shape. Further, at an initial stage of thedrilling operation, a rotational center of the drilling blades 15 ispositioned by mounting a center pin at a center of the core drill 10.Chips P produced by cutting by the drilling blades 15 are moved into thechip evacuating groove 16, pushed up to the upper side gradually by thechips P successively produced by the drilling blades 15 and evacuated tothe surface of the concrete. Although air on the inner side of the coremain body 14 is compressed in accordance with progress of drilling, airis exhausted to the outer side of the core main body 14 via the opening18 and the drilling efficiency is not hampered by compressed air.Further, when drilling is further progressed and the core main body 14is immerged in the concrete C to a portion of the opening 18, by theflow of exhausting compressed air, chips at inside of the chipevacuating groove 16 are helped to evacuate to the upper side andtherefore, chips are evacuated excellently. Further, concrete powderdust remaining at a space on the inner side of the core main body 14 isexhausted to outside from the opening 18 and therefore, a resistanceagainst rotation which is brought about by storing the powder dust atthe inner side space is nullified, loss in rotating the core main body14 is reduced and drilling can be carried out efficiently.

FIG. 4 shows the core drill 20 according to other embodiment of theinvention and although the embodiment is the same as the above-describedembodiment in that the outer peripheral face of the core main body 14 isformed with a plurality of the chip evacuating grooves 26 in parallelwith a rotational axis line of the core drill 20, the chip evacuatinggroove 26 of the embodiment is cut to form such that a depth of thegroove is formed to be the same from a lower end to an upper end thereofand a groove width of the chip evacuating groove is gradually increasedsuch that a groove width W2 at an upper end portion thereof is widerthan a groove width W1 at a lower end portion of the core main body 14to thereby form the chip evacuating groove such that a sectional area ofthe chip evacuating groove 26 is gradually increased from the lower endto the upper end. Therefore, chips produced by the drilling blades 15are pushed up to the upper side of the chip evacuating groove 26 havinga large sectional area and therefore, chips are not clogged at inside ofthe chip evacuating groove 26 and evacuation is carried out excellently.

FIG. 5 shows the core drill 30 according to still other embodiment ofthe invention which is formed such that the chip evacuating groove 36formed at the outer peripheral face of the core main body 14 is formedsuch that a sectional area thereof is gradually increased from a lowerend side to an upper end thereof to thereby prevent chips from beingclogged at inside of the chip evacuating groove 36. According to theembodiment, the chip evacuating groove 36 is formed by cutting in aspiral shape along the outer peripheral face of the core main body 14such that a depth of the chip evacuating groove 36 is gradually deepenedfrom a lower end to an upper end thereof. According to the chipevacuating groove 36 of the embodiment, different from the chipevacuating groove in the spiral shape according to the background art, aplurality of streaks of the chip evacuating grooves 36 in the spiralshape increasing the spiral pitch are arranged in the circumferentialdirection at equal intervals along the outer peripheral face of the coremain body 14 to thereby facilitate to evacuate chips produced by thedrilling blades 15 to the upper side.

FIG. 6 shows the core drill 40 according to still other embodiment,similar to the above-described embodiment shown in FIG. 1, the chipevacuating grooves 46 a in the vertical direction in parallel with therotational axis line are formed at the outer peripheral face of the coremain body 14 at equal intervals in the peripheral direction and aplurality of streaks of the chip evacuating grooves 46 b in the spiralshape similar to those of the embodiment shown in FIG. 5 are formed tointersect with the chip evacuating grooves 46 a in the verticaldirection. By forming the chip evacuating grooves 46 a, 46 b in thisway, evacuation of chips to the upper side is further improved byoperation of rotating the portion of the core main body 14.

In any of the above-described embodiments, by forming diamond abrasivegrain layers on an outer surface of the core main body 14 formed toarrange among the chip evacuating grooves 16, 26, 36, 46 a, 46 b,bringing the abrasive grain layers into contact with chips produced bythe drilling blades 15 to further finely polish chips to further makeevacuation of chips effective and bringing the diamond abrasive grainlayers into contact with an object to be cut of concrete or the like,the resistance against rotation can be reduced and further excellentcutting operation can be carried out.

FIG. 7 shows an example of forming a slender groove 36 a from the lowerend portion to the upper end portion of the core main body 14 on theouter peripheral face between the contiguous chip evacuating grooves 36.A plurality of the slender groove 36 a may be provided. Accordingthereto, a contact area between the outer peripheral face of the coremain body 14 and concrete is reduced and therefore, the resistanceagainst rotation is reduced, the rotational speed can be maintained andthe high drilling function can be ensured.

Further, the similar slender groove 36 a can be formed at the outerperipheral face between the contiguous chip evacuating grooves 16 or 26also in the examples of FIG. 1 and FIG. 4.

Further, FIG. 8 shows an example of forming a lateral groove 36 b in thecircumferential direction of the core main body 14 to the outerperipheral face between the contiguous chip evacuating grooves 36. Thelateral groove 36 b is formed along the rotational direction, thecontact area between the outer peripheral face of the core main body 14and concrete is reduced and therefore, also in this case, the resistanceagainst rotation is reduced, the rotational speed can be maintained andthe high drilling function can be ensured.

Further, the similar lateral groove 36 b can be formed at the outerperipheral face between the contiguous chip evacuating grooves 16 or 26also in examples of FIG. 1 and FIG. 4.

Next, still other embodiment of the invention will be explained. Asshown by FIG. 9, similar to the above-described embodiment, the coredrill 50 according to the embodiment is constituted by the shank 11coupled to a rotating tool, and the drill main body 12 attached to thelower end portion of the shank 11 and the drill main body 12 isconstituted by the core main body 14 in the cylindrical shape the upperend portion 13 of which is closed and the drilling blade 15 attached tothe lower end edge of the core main body 14. The outer peripheral faceof the core main body 14 is formed with a plurality of the chipevacuating grooves 51 extended in the vertical direction in parallelwith the rotational axis of the core drill 50 at predetermined intervalsin the peripheral direction. Further, the chip evacuating groove 51 iscut such that the depth of the upper end portion 13 becomes graduallylarger than that of the lower end portion proximate to the drillingblades 15 and formed such that a sectional area of the chip evacuatinggrooves 51 is gradually increased to the upper side. Thereby, chipsproduced by the drilling blades 15 are prevented from being clogged atinside of the chip evacuating groove 51. A bottom of the chip evacuatinggroove 51 is formed with the opening 18 for communicating inside andoutside of the cylinder of the core main body 14. Also the effect by theopening 18 is as described above.

Further, a number of the projections 52 are formed at the outerperipheral face of the core main body 14 between the contiguous chipevacuating grooves 51 of the core main body 14 of the core drill 50according to the embodiment from the lower end portion to the upper endportion of the core main body 14. As shown by FIGS. 10(a), 10(b) and10(c), the projection 52 is formed in a shape of a triangular pyramidand the top portion 53 is projected in a radial direction of the coremain body 14 and the top portion 53 of the projection 52 is brought intocontact with an inner peripheral face of a concrete hole bored by thedrilling blades 15. The projection 52 can be formed at the outerperipheral face of the core main body 14 by means of welding or thelike. By bringing the top portion 53 of the projection 52 into contactwith the inner peripheral face of the concrete hole bored by thedrilling blade 15, a total of the outer peripheral face of the core mainbody 14 is not brought into contact with the inner peripheral face ofthe concrete hole. Therefore, the friction resistance in rotating thecore drill 50 is reduced and the rotational speed of the core drill canbe prevented from being reduced.

FIG. 11 shows the core drill 60 according to still other embodiment andaccording to the embodiment, a plurality of streaks of the chipevacuating grooves 61 in the spiral shape are formed at the outerperipheral face of the core main body 14 along the outer peripheral faceof the core main body 14 at equal intervals in the circumferentialdirection and the chip evacuating grooves 61 are formed such that asectional area of the chip evacuating groove 61 is gradually increasedfrom a lower end side to an upper end thereof to thereby prevent chipsfrom being clogged at inside of the chip evacuating groove 61.

A number of the projections 62 are formed at the outer peripheral faceof the core main body 14 between the contiguous chip evacuating grooves61 of the core drill 60 from the lower end portion to the upper endportion of the core main body 14. As shown by FIGS. 12(a), 12(b) andFIG.(c), the projection 62 is formed in a shape of a pyramid a bottomface of which is formed in a rectangular shape or a rhombic shape andformed to project the top portion 63 of the projection 62 from the outerperipheral face of the core main body 14 in the radial direction. Bybringing the top portion 63 of the projection 62 into contact with theinner peripheral face of the concrete hole bored by the drilling blades15, a total of the outer peripheral face of the core main body 14 is notbrought into contact with the inner peripheral face of the concrete holeto thereby reduce the friction resistance in rotating the core drill 60.

Although in the above-described embodiments, an explanation has beengiven by the embodiments in which the chip evacuating grooves 51, 61formed at the outer peripheral face of the core main body 14 are formedin parallel with the center axis line of the core drill or in the spiralshape, the shape and the structure of the chip evacuating groove may beconstituted by any of the embodiments, further, a groove in the verticaldirection and a groove in the spiral shape may be integrated to form asin the embodiment shown in, for example, FIG. 6. Further, the shape ofthe projection is not limited to the shape of the triangular pyramid andthe shape of the pyramid but as shown by FIGS. 13(a), 13(b) and 13(c),the shape may be formed by the projection 70 in a shape of a circularcone projecting the top portion 71 thereof in the radial direction, or,as shown by FIGS. 14(a), 14(b) and 14(c), the shape may be formed by theprojection 72 in a semispherical shape bulging the top portion 73 in aspherical shape in the radial direction. Further, two or more of shapesin the shape of the triangular pyramid, the shape of the pyramid, theshape of the circular cone and the semispherical shape may be combined.

Further, the invention is not limited to the above-described embodimentsbut can variously be modified within the technical range of theinvention and the invention naturally covers the modifications.

The application is based on Japanese Patent Application Japanese PatentApplication No. 2002-010740) filed on Jan. 18, 2002, Japanese PatentApplication (Japanese Patent Application No. 2002-306664) filed on Oct.22, 2002 and Japanese Patent Application (Japanese Patent ApplicationNo. 2003-003646) filed on Jan. 9, 2003 and contents thereof areincorporated here by reference.

INDUSTRIAL APPLICABILITY

According to the core drill of the invention, by forming the chipevacuating groove in parallel with the shaft of the core main body, incomparison with the groove formed in the spiral shape of the backgroundart, fabricating steps are simplified and fabrication cost or the likecan be reduced.

Further, by forming the core drill according to the invention such thatthe sectional area of the chip evacuating groove is gradually increasedfrom the lower end to the upper end, in pushing up chips at inside ofthe chip evacuating groove to the upper side by chips produced by thedrilling blades, chips are pushed up in a direction of widening thesectional area of the groove and therefore, chips are not clogged atinside of the chip evacuating groove, chips are evacuated excellentlyand chips can be prevented from constituting the resistance againstrotation of the core drill. Therefore, the drilling efficiency can bepromoted.

Further, according to the core drill of the invention, by forming theopening for communicating inside and outside of the core main body atthe bottom of the chip evacuating groove, the concrete powder dustremaining at the inner side space of the core main body 14 is evacuatedto outside from the opening 18 and therefore, the resistance againstrotation produced by storing the powder dust in the inner side space iseliminated, loss in rotating the core main body 14 is reduced anddrilling can be carried out efficiently.

Further, by forming the chip evacuating groove in the spiral shape atthe outer peripheral face of the core main body, chips produced indrilling can be facilitated to evacuate to the upper side.

Further, by forming the slender groove or the lateral groove at theouter peripheral face between the contiguous chip evacuating grooves inthe core drill according to the invention, the contact area between theouter peripheral face of the core main body 14 and concrete is reducedand therefore, the resistance against rotation is reduced, therotational speed can be maintained and the high drilling function can beensured.

Further, in the core drill of the invention, by forming a number of theprojections projected from the outer peripheral face of the core mainbody in the radial direction at the outer peripheral face of the coremain body between the chip evacuating grooves formed at the core mainbody, the top portions of the projections projected in the radialdirection are brought into contact with the inner peripheral face of theconcrete hole bored by the drilling blades, the friction resistance bybringing the total face of the core main body into contact with theinner peripheral face of the concrete hole can be prevented from beingincreased and the drilling function by reducing the rotational speed ofthe core drill can be prevented from being reduced.

1. A core drill comprising: a shank connected to a rotating tool at anupper end thereof; a core main body in a cylindrical shape attached to alower end of the shank; a drilling blade provided at a lower end edge ofthe core main body; and a plurality of chip evacuating grooves formedfrom a lower end portion to an upper end portion of an outer peripheralface of the core main body and formed in parallel with a rotational axisof the core main body and at intervals in a peripheral direction.
 2. Thecore drill according to claim 1, wherein the chip evacuating groove isformed such that a sectional area thereof is gradually increased fromthe lower end portion to the upper end portion of the outer peripheralface of the core main body.
 3. The core drill according to claim 1,further comprising: a spiral chip evacuating groove formed in a spiralshape at the outer peripheral face of the core main body.
 4. The coredrill according to claim 1, wherein an opening for communicating insideand outside of the core main body is formed at a bottom of the chipevacuating groove.
 5. A core drill comprising: a shank connected to arotating tool at an upper end thereof; a core main body in a cylindricalshape attached to a lower end of the shank; a drilling blade provided ata lower and edge of the core main body; and a plurality of chipevacuating grooves formed from a lower end portion to an upper endportion of an outer peripheral face of the core main body and formed atintervals in a peripheral direction; wherein the chip evacuating grooveis formed such that a sectional area of the chip evacuating groove isgradually increased from the lower end portion to the upper end portionof the outer peripheral face of the core main body.
 6. The core drillaccording to claim 5, wherein the chip evacuating groove is formed in aspiral shape at the outer peripheral face of the core main body.
 7. Thecore drill according to claim 5, wherein an opening for communicatinginside and outside of the core main body is formed at a bottom of thechip evacuating groove.
 8. The core drill according to claim 5, furthercomprising: a slender groove formed at the outer peripheral face of thecore main body between contiguous ones of the chip evacuating groovesand from the lower end portion to the upper end portion of the core mainbody.
 9. The core drill according to claim 5, further comprising: alateral groove formed at the outer peripheral face of the core main bodybetween contiguous ones of the chip evacuating grooves and in acircumferential direction of the core main body.
 10. A core drillcomprising: a shank connected to a rotating tool at an upper endthereof; a core main body in a cylindrical shape attached to a lower endof the shank; a drilling blade provided at a lower end edge of the coremain body; a plurality of chip evacuating grooves formed from a lowerend portion to an upper end portion of an outer peripheral face of thecore main body and formed at intervals in a peripheral direction; and aplurality of projections projected at the outer peripheral face of thecore main body between contiguous ones of the chip evacuating groovesand in a radial direction from the outer peripheral face of the coremain body.
 11. The core drill according to claim 10, wherein the chipevacuating groove is formed in parallel with a rotational axis of thecore main body.
 12. The core drill according to claim 10, wherein thechip evacuating groove is formed in a spiral shape at the outerperipheral face of the core main body.
 13. The core drill according toclaim 10, wherein the projection comprises at least one of a shape of atriangular pyramid, a shape of a pyramid, a shape of a circular cone anda semispherical shape.